I have a reseller account to host my clients, but I'm thinking to move to dedicated server, and I'm really confused on DNS/IP issues.

Currently, I have my own name server like

And my client uses different shared IP:

If I get a dedicated server, and still using my reseller account ('cause it's a pain to move all of my clients over), but I want to use the same DNS which are ns1.mydomain.com, and ns2.mydomain.com, can I do that? and how?

Can I register another name server without getting a new domain?

If I get my dedicated server, and decide to sell plans to other resellers, each reseller will have 2 IPs, and all resellers will share 1 shared IP for all clients, how can I do that?

Thanks for your help